WASHINGTON — The military might have to pick up the slack if a spat over President Donald Trump’s demands for border wall funding forces a partial government shutdown later this month.

With the military funded into late 2019, the Defense Department might have to fill in the gaps for agencies that aren’t, such as the Department of Homeland Security, which includes the Transportation Security Administration and Immigration and Customs Enforcement.

The Defense Department, along with 75 percent of the government, saw its fiscal year 2019 budget approved earlier this year. But the remaining agencies are still awaiting approval for their spending plans.

“If DHS had to scale back its activities on the border, DoD might have to step up its activities,” said Mark Cancian, a senior adviser with the Washington think tank Center for Strategic and International Studies. For example, “if for some reason TSA had to reduce its operation … you could imagine the military being ordered to support or conduct security at airports.”

A possible, partial shutdown slated for Friday could be delayed as a result of Washington ceremonies to honor former President George H.W. Bush. Trump has said he would approve a plan to push the funding deadline to Dec. 21 as a result of a series of memorials honoring Bush, who died Friday.

Moreso, House lawmakers introduced the two-week measure Monday, and the legislation was poised to win approval this week. However, Trump did not let up Tuesday on his demands for $5 billion in funding for the U.S.-Mexico border wall.

“Get it done!” Trump tweeted Tuesday morning, in addition to dubious claims that the wall would pay for itself or blaming massive U.S. financial losses on illegal immigration.

This isn’t the first time that Trump has threatened a shutdown over massive funding for a border wall, but it’s been to no avail in past efforts.

As a result, Cancian and other experts suggest the odds are low for a partial shutdown because both parties fear backlash from the public with such a move.

“He threatens it every year,” Cancian said of Trump’s shutdown threats. So, “odds seem to be relatively low.”

Other pundits are also betting against such a move, agreeing the political price remains too high. And a previous appropriations measure already included $1.6 billion in border security funding that has yet to be spent, some Trump critics have said.

“We are dealing with Donald Trump, who is emotional and changeable in his intentions and actions. … I would say it’s less than likely, but certainly possible,” said Ben Friedman, a fellow for Defense Priorities, a right-leaning Washington think tank. “It sure seems like a political loser for the president.”

Impact on the military

Molly Reynolds, a governance studies fellow at the Brookings Institution, a liberal-leaning Washington think tank, also sees a small chance for a partial shutdown.

“I continue to think that a shutdown is relatively unlikely. I expect them to reach some sort of deal,” Reynolds said. But “if there is a partial shutdown, the military will be largely unaffected.”

Andrew Sherbo, a University of Denver finance professor who has tracked government and defense budget issues, agreed, if there is a shutdown, it could have no impact on the military.

“I do recall an earlier shutdown where DoD had the appropriation bill passed, and other government agencies did not, and it was business as usual for DoD,” he said.

Friedman said if there is an impact on the military, it will depend on how long the shutdown lasts. The longer it is, the more likelihood it could affect service members who might be assigned to fill gaps in other departments.

Cancian suggested one scenario could be the Defense Department taking on functions for Homeland Security, with service members expanding their authorities in their deployment along the U.S.-Mexico border.

“I think the three big areas would be border patrol, ICE and TSA,” he said. “If for some reason they could not operate, or could not fully operate, the military may be ordered in as a stop gap.”

This could include functions involving temporary detention and riot control efforts.

“DoD might have to step in and implement some of those authorities that [Defense Secretary Jim] Mattis was given but not yet exercised,” Cancian said.

For TSA, the military could have to revisit duties that they provided following the 9/11 attacks, such as airport security.

It’s also possible that these agencies will have enough miscellaneous funding to get through a short shutdown, thus not requiring additional military support, Cancian noted. For example, frequent flyer programs such as TSA PreCheck give that agency additional funds that could be used during a shutdown.

“TSA may have enough money to get through a few days,” he said. “The rules here are very complicated because if an agency has an independent source of money, it can use that money to keep operating for at least a limited period of time.”

Smaller share of government faces shutdown threat

In September, a fiscal year 2019 spending package of more than $850 billion to fund defense, labor, health and human services and other related agencies was passed into law. That same month, a smaller appropriations measure funding veterans affairs, military construction and other efforts was also approved.

The Defense Department “is OK as the [fiscal year] 2019 DoD appropriations bill … became public law” when Trump signed the legislation Sept. 28, 2018, said Sherbo. “Five of the 12 annual [fiscal year] 2019 appropriation bills are public law as of today,” including the departments of Defense, Veterans Affairs, Energy, Labor, Health and Human Services and Education.

The larger defense measure, H.R. 6157, also included temporary appropriations funding, known as a continuing resolution, for the remaining agencies still lacking funding for the 2019 fiscal year, which started Oct. 1. The continuing resolution funded agencies until Dec. 7.

Now, in addition to Homeland Security, the departments of Justice, State, Commerce, Agriculture and Financial Services are among the agencies at risk of closure, said Sherbo, a former Pentagon official.

“Seven [fiscal year] 2019 bills are not OK and face shutdown,” he said. And “the Homeland Security appropriation includes the $5 billion for the border wall, which is at the heart of the potential shutdown.”

Now, political leaders are on the hook to pass a spending measure to fund these agencies to avert the partial, government shutdown. Following the death of the Bush on Friday, Trump said the next day that he would consider a two-week delay to the shutdown.

The funding fight is poised to play out closer to the Christmas holiday.

“If they [Congress] come to me … to talk about an extension because of President Bush’s passing, I would absolutely consider it and probably give it,” Trump said Saturday aboard Air Force One.